CHARACTERISTIC MODE ANALYSIS OF ANTENNA

Transcription

1 Volume 118 No ISSN: (on-line version) url: CHARACTERISTIC MODE ANALYSIS OF ANTENNA 1 Sundaramoorthy A, 2 John Wiselin, 3 Sreeja B S, 3 Manikandan E, 3 Roobini A 1 Research scholar, Bharath University, Chennai, India 2 Department of EEE, Vidhya Institute of Science and Technology, Trivandrum, India 3 Department of ECE, SSN College of Engineering, Chennai, India, May 24, 2018 Abstract The main objective is to design different types of antenna with the desired radiation characteristics using the most effective design methods. It is used to obtain numerical approach for antenna design and predicting radiating behaviour of antenna by analysis of characteristic modes. The theory of characteristics mode is used to synthesize desired current distribution and radiating behavior of an antenna. The surface current distribution of different modes of antenna identifies the optimum feeding point for the designed antenna. The designed antenna may operate at multiple standards so it may provide multiband or broadband operation. It may be facilitate orthogonal radiation patterns at 1

2 a given frequency of multiple characteristic modes, which provide effective multiple input multiple output (MIMO) antennas. Key Words:Theory of characteristic modes (TCM), Modal analysis, microstrip antenna, reflection coefficient, current distribution, radiation pattern. 1 Introduction At present antenna design is essentially utilized on commercial applications, especially cellular telephony systems and wireless systems. The proposing new antennas are mainly devoted to describe the antenna geometry and its radiating behavior, while the design procedure does not match the requirement and considerations, therefore the problems have to limit. Their problem is that the physical accuracy is less, so the operating principles of the antenna are mislaid. The theory of characteristic modes (TCM) gives the number of current distribution and radiation pattern with respect to the different modes of frequency. The theory of characteristic modes was first introduced by Garbacz [1] and later developed by Harrington and Mautz [2]. A procedure for conducting bodies of arbitrary shape is developed [3]. Then the theory of characteristic modes is revisited for modern applications designed antenna [4].The modal analysis is proposed for multiple input multiple output (MIMO) applications [5-7]. Using this technique, both multiband resonance and bandwidth is achieved [8]. This analysis is also used for performance improvement of circularly polarized slotted patch antenna [9].Characteristic mode analysis (CMA) can be used to optimize the shape of antenna, to improve the antenna topology, decide on the antenna placement and synthesize a desired antenna pattern for ultra wideband (UWB) transverse electromagnetic (TEM) horn and long term evolution (LTE) antenna using FEKO [10]. The analysis of eigen current distribution gives new feeding techniques. This technique will be of help to design compact ultra wideband antenna for chip integrating transceivers [11]. The characteristic mode is equivalent to the method of moments (MoM) equations using the singular value decomposition and later by its special case of spectral decomposition of matrix [12]. A new method of tracking procedures is introduced for theory of charac- 2

3 teristic mode [13]. The MoM antenna is simulated with MATLAB using Rao-Wilton-Glisson (RWG) basis functions [14] and [15]. The modal methods are also used to design complicated shapes like fractal patch antenna [16]. The effects of ground plane size, effects of slot on the notched frequency characteristics and effects of miniaturization of monopole antenna is analyzed with the help of different modes of antenna [17]. The rest of the portion is organized as follows: Section II briefly reviews the theory of characteristic mode and flow chart of TCM. In Section III, IV and V, the design of antenna, reflection coefficient, current distribution and radiation pattern of the different modes of rectangular, circular and hexagonal shape of antennas are explained. Finally, some conclusions are given in Section VI. 2 THEORY OF CHARACTERISTIC MODES The theory of characteristic modes (TCM) gives the number of current distribution and radiation pattern with respect to the different modes of frequency. The current distribution which is dependent upon eigen value and eigen vector. The mathematical formulation of characteristic modes that relates the current on conducting body as explained in [2], [L(J)E i ] tan = 0 (1) where tan denotes the tangential components on the surface S. The operator L in (1) is linear and it is defined by L(J) = jωa(j) + Φ(J) (2) where A (J) and Φ (J) are vector and scalar potentials respectively. Physically, the term L (J) can be considered as the electric intensity at any point in space. This means that the operator L in (1) has the dimension of impedance: Z(J) = [L(J)] tan (3) As drawn from [1], the impedance operator Z is complex, and it can be written as, Z(J) = R(J) + jx(j) (4) 3

4 The Characteristic current modes are obtained from the eigen value linear equation which is given as X (J n ) = λ n R (J n ) (5) where R and X are Real and imaginary parts of impedance operator Z=R+jX, λ n is eigen value, (J n )is eigen function. It is defined as the real currents on the surface of a conducting body that depends on shape and size. Thus design of antenna using theory of characteristic modes can be performed in way of: Characteristic current and associated characteristic fields are calculated. By the eigen values, determine the resonance frequency of the modes. The shape and size is modified until the desired frequency is obtained. At last, studying the current distribution of modes and obtain specific radiating field. Fig.1. represents the flow chart of theory of characteristic modes (TCM). Fig.1. Flow chart of TCM 3 RECTANGULAR PATCH Microstrip antenna is used for the applications such as aircraft, automobile vehicles and wireless applications. Microstrip antenna 4

5 consists of dielectric substrate, a radiating patch on one side and a ground plane on the other side. Microstrip antennas are also referred to as patch antennas. The frequency of operation of the patch antenna is determined by the length L. The width W of the microstrip antenna controls the impedance on antenna feed. The radiation in microstrip patch antenna is along the width and not along the length of the patch. The electric field is zero at the middle of the patch, maximum at one side, and minimum on the opposite side. A. Design of Rectangular patch The rectangular patch is designed for 2.4 GHZ. The dimension of the rectangular patch depends on the length and width of the patch. The width of the microstrip patch antenna controls the impedance across the input. Larger width can also increase the bandwidth. Fig.1. illustrates the geometry of rectangular patch. Table I represents the dimensions of rectangular patch. The design calculation is given as follows: Frequency, f = 2.4 GHz Permittivity of FR4 substrate, ɛ r = 4.3 Height of FR4 substrate, h=1.6mm a)w idthof thep atch, Width of the Patch, W = 2f c ɛ r+1 2 = / W = 38.39mm (6) b) Length of the Patch, L= L eff 2 L Wavelength, λ = c f = = 125mm Effective dielectric constant, ɛ eff = ɛ r = (0.8164) + ɛ r 1 [1 + 12h/w] 1/2 2 5

6 = Length Extension, L = mm Effective length, L eff = = 0.412h (ɛ eff+0.3)( w h ) (ɛ eff )( w h + 0.8) c 2f ɛ r = mm Length of the patch, L = L eff 2 L L= (0.7412) Length of the patch, L= mm (7) c) Feed length = λ 4 ɛ r = 31.25/ 4.3 Feed length = 15mm (8) d) Feed width = 3 mm (For Characteristic impedance Z o = 50Ω) Fig.2. Rectangular Patch TABLE I. Dimensions of Rectangular patch B. Simulated Result Fig.3. shows the current schematics of the six Eigen modes. Fig.4. shows the return loss of the rectangular patch. The return loss is obtained at -15 db around 2.4 GHz. It covers applications of Bluetooth ( GHz) and S band (2 4 GHz). 6

7 Fig.3. Current schematics for the six Eigen vectors Fig.4. Return loss of Rectangular patch C. Modal Analysis The modal analysis which describes the current distribution and radiation pattern of different modes of resonant frequency. The Surface current of different modes of antenna is obtained by Eigen mode solver. It calculates the eigen values (resonant frequencies) and eigen modes (field patterns). TABLE II. Modal analysis of Rectangular patch 7

8 Table II represents the modal analysis of rectangular patch. The first mode J1 has current distribution near the feed point. It has less radiating behaviour. So this resonant frequency is not considered for antenna design. The second mode J2 has vertical currents. It has omnidirectional radiating pattern. The third mode J3 has high current distribution along z axis. It has omnidirectional pattern. J4, J5 and J6 resonate at higher frequencies and the radiation is varied with respect to the resonant frequency. 4 CIRCULAR PATCH The circular patch antenna consists of radiating patch, ground plane and the substrate material between the two planes. The circular patch of the antenna depends on the radius of the patch. It controls the modes of the antenna. A. Design of Circular Patch The circular patch is designed for 3.5 GHZ. The dimension of the rectangular patch depends on the radius of the patch. Fig.5. illustrates the geometry of circular patch. Table III represents the dimensions of circular patch. The design calculation is given as follows: Radius of patch, 8

9 F a = 2h {1 + πaɛ r[ln( πa 2h )] }1/2 Radius of patch, a= 12mm where F = f r ɛr The microstrip line is designed for impedance of 50 in order to match the feed line impedance which is given as w h = 2 π [B 1 ln(2b 1) + ɛ r 1 (ln(b 1) )] 2ɛ r ɛ r h - Thickness of substrate w - Width of microstrip line ɛ- Dielectric constant of the substrate Z 0 - Input impedance B = 60π2 Z 0 ɛr Fig.5. Circular Patch TABLE III. Dimensions of Circular patch 9

10 B. Simulated Result Fig.6. shows the return loss of the circular patch. The 10dB return loss bandwidth is from 3.5GHz to 5.8 GHz. It gives wide bandwidth. It covers applications of WiMax (3.3 4GHz) and C band (4-8 GHz). Fig.6. Return loss of Circular patch Modal Analysis Table IV represents the modal analysis of circular patch. The first mode J 1 has current distribution near the feed point. It has less radiating behaviour. So this resonant frequency is not considered for antenna design. The second mode J 2 has vertical currents. It has omnidirectional radiating pattern. The third mode J 3 has high current distribution along z axis. It has omnidirectional pattern. J 4, J 5 and J 6 resonate at higher frequencies and the radiation is varied with respect to the resonant frequency. The radiation pattern of all higher frequencies is directional and current distribution is better so it has return loss of less than 10dB. The spectrum gives wide bandwidth. TABLE IV. Modal analysis of Circular patch 10

11 5 HEXAGONAL PATCH The configuration of the hexagonal patch antenna is shown in Fig.7. withw 2 =12mm, L s =36mm, W s =34mm, substrate thickness h=1.6mm, dielectric constant ɛ r =4.3. Table V represents the dimensions of hexagonal patch. Fig.7. Hexagonal Patch TABLE V. Dimensions of Hexagonal patch A. Simulated Result Fig.8. shows the return loss of the hexagonal patch. The 10dB return loss bandwidth is from 3.8 GHz to 10.6 GHz. It gives ultra 11

12 wide bandwidth. It covers applications of WiMaX (3.3 4GHz) and C band (4-8 GHz). Fig.8. Return loss of Hexagonal patch B. Modal Analysis Table VI represents the modal analysis of hexagonal patch. The first modej 1 has current distribution near the feed point. It has less radiating behaviour. So this resonant frequency is not considered for antenna design. The second mode J 2 has vertical currents. It has omnidirectional radiating pattern. The third mode J3 has high current distribution along z axis. It has omnidirectional pattern. J 4, J 5 and J 6 resonate at higher frequencies and the radiation is varied with respect to the resonant frequency. The radiation pattern of all higher frequencies is directional and current distribution is better so it has return loss of less than 10dB. The spectrum gives ultra wide bandwidth. TABLE VI. Modal analysis of Hexagonal patch 12

13 6 CONCLUSION The different types of antennas have been presented, with the aim of review the theory of characteristics mode and demonstrating the analysis of characteristic mode. In contrast to other classical design methods, characteristic modes bring physical insight into the current distribution and radiating behavior of the antenna. It is used to identify new shape of the antenna and gives a desired antenna pattern. This technique is used for multi band, ultra wide band and MIMO applications. References [1] R.J.Garbacz and R.H.Turpin,A generalized expansion for radiated and scattered fields, IEEE Transaction on Antennas and propagation.,vol.ap-19,may 1971,pp [2] R.F.Harrington and J.R.Mautz, Theory of Characteristic Modes for Conducting Bodies, IEEE Transactions on Antennas and Propagation, AP-19, 5, September 1971, pp [3] R.F.Harrington and J.R. Mautz, Computation of Characteristic Modes for Conducting Bodies, IEEE Transactions on 13

14 Antennas and Propagation, AP-19, 5, September 1971, pp [4] Marta Cabedo Fabres, Eva Antonino-Daviu, Alejandro Valero Nogueira and Miguel Ferrando Bataller,The theory of characteristic modes revisited: A contribution to the design of antennas for modern applications, IEEE Antennas and Propagation Magazine, Vol. 49, No. 5, pp.52,68, October [5] Ali Araghi and Gholamreza Dadashzadeh, Oriented design of an antenna for MIMO applications using theory of characteristic modes, IEEE Antennas And Wireless Propagation, Vol. 11, pp.1040,1043, [6] Hui Li, Yi Tan, Buon Kiong Lau, Zhinong Ying and Sailing He, Characteristic mode based trade off analysis of antenna chassisi interactions for multiple antenna terminals,ieee Transactions On Antennas And Propagation, Vol. 60, No. 2, pp.490,502, February [7] Martens, R.; Manteuffel, D., Systematic design method of a mobile multiple antenna system using the theory of characteristic modes, in Microwaves, Antennas & Propagation, IET, vol.8, no.12, pp , Sept [8] Zachary Miers,Hui Li and Buon Kiong Lau,Design of bandwidth-enhanced and multiband MIMO antennas using characteristic modes, IEEE Antennas And Wireless Propagation, Vol. 12,No.2, pp.1696,1699, [9] Y. Chen and C.-F. Wang, Characteristic-mode-based improvement of circularly polarized U-slot and E-shaped patch antennas,ieee Antennas Wireless Propag. Lett, Vol. 11, pp , Dec [10] Martin Vogel, Gopinath Gampala, Daniel Ludick, Ulrich Jakobus and C. J. Reddy, Characteristics mode analysis: putting physics back into simulation,ieee Antennas and Propagation Magazine, Vol. 57, No. 2, pp.307,317, April [11] Ahme Toaha Mobashsher and Amin Abbosh, Utilizing Symmetry of Planar Ultrawideband Antennas for Size Reduction 14

15 and Enhanced Performance, IEEE Antennas and Propagation Magazine, Vol. 57, No. 2, pp.153,156 April [12] Pavel Hazdra, Pavel Hamouz, On The Modal Superposition Lying Under The MoM Matrix Equations., Radioengineering, Vol. 17, No. 3, September [13] M. Capek, P. Hazdra, P. Hamouz, and J. Eichler, A method for tracking characteristic numbers and vectors, Progr. Electromagn. Res. B,vol. 33, pp , [14] Makarov, S., MoM antenna simulations, with Matlab: RWG basis functions, IEEE Antennas and Propagation Magazine, IEEE, vol.43, no.5, pp , Oct 2001 [15] Capek, M.; Hamouz, P.; Hazdra, P.; Eichler, J., Implementation of the Theory of Characteristic Modes in MATLAB, IEEE Antennas and Propagation Magazine, IEEE, vol.55, no.2, pp , April 2013 [16] J. Eichler, P. Hazdra, M. Capek, T. Korinek, and P. Hamouz, Design of a dual-band orthogonally polarized L-probe-fed fractal patch antenna using modal methods, IEEE Antennas Wireless Propag. Lett., vol. 10, pp , Dec [17] W. Wu and Y. P. Zhang, Analysis of ultra-wideband printed planar quasi-monopole antennas using the theory of characteristic modes, IEEE Antennas Propag. Mag., vol. 52, no. 6, pp. 6777, Dec